Core portions having fused bond joint outside of embrace of coils thereon



Sept. 26, 1967 P. G. ABERIZK 3,344,383'

CORE PORTONS HAVING FUSED BOND JOINT OUTSIDE OF EMBRACE OF COILS THEREON Filed Dec. 30, 1965 IH w jV/P 2% N WM'W':

United States Patent O 3 344 383 CORE PORTIoNs HAVING FUSED BOND JOINT OUTSIDE F EMBRACE 0F COILS THEREON Philip G. Aberizk, Methuen, Mass., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Dec. 30, 1965, Ser. No. 517,649 7 Claims. (Cl. 336-160) ABSTRACT 0F THE DISCLOSURE An electromagnetic ballast with two three-legged core portions formed of laminated strips interleaved to form an O-shaped core with air gaps between spaced ends of the strips adjacent t-he interleaf, the core portions being secured together by a fused bond joining outer, butted strips, different sized coils wound around the core legs, and magnetic shunt straps bridging parallel legs of the core in a zone coextensive with the interleaf, the air gaps being located outside said zone.

A typical laminated metal core comprises two generally I- or U-shaped portions each formed of thin strips of ferromagnetic metal. The strips, graduated in length, are bent into .lor U-shape and nested within the outer bent strip to form the core portion. Adjacent ends of the strips of one core portion are staggered for interleang and butt-engagement with the en-ds of the strips of the other core portion. When joined, the two core portions form a rectangular, generally O-shaped flux path having two pairs of parallel legs around a coil space. Two or more coils, in the case of a transformer, are wound around legs of the core portions, or preformed and slipped on the core legs, with the coil axes parallel to the core legs, prior to joining the core portions. The two portions are then secured together, and in some cases a magnetic shunt strap is welded to the joined core portions in a zone between two parallel legs. The shunt reforms the single, O-shaped ux path into two flux paths, of figure-8 construction, the shunt being common to both paths.

For many purposes it is desirable that the end of every strip in one core portion tightly butt against every strip end of the other core portion. On the other hand, in some cases there is an advantage in leaving an air gap between opposed strip ends. For example, certain ballasts for fluorescent lamps perform more effectively if the current in their secondary winding leads the voltage `across the winding. Such current lead may be produced by providing air gaps in the flux path of the winding between the ends of the core strips. However, with previous laminated strip cores provision of a shunt and air gap has interfered with the selection of desired coil sizes, an-d it is an object of the present invention to provide an inductor core of improved construction wherein the magnetic shunt may be optimally located for coils of varying size ratios without interfering with the function of the air gaps.

According to the invention, an inductor comprises two U-shaped magnetic metal core portions forming legs joined to surround a coil space, a plurality of coils of different axial lengths embracing at least one leg of each group, and extending through different par-ts of said coil space, each said core portion comprising at least three U-shaped strips including an outer strip and inner strips nested within said outer strip, the ends of the strips of one Iportion being staggered for interleang and butteng-agement with the ends of the strips of the other portion, the outer strips of the two core portions being in butt-engagement and joined by a fused bond to secure the portions together, at least one of the inner strips of one portion being spaced endwise from a strip of the other 3,344,383 Patented Sept. 26, 1967 ICC portion to form an air gap therebetween, and a magnetic shunt body extending between parallel legs of said core portions in a zone `coextensive with the interleang ends of the strips, said air gap being located outside said zone.

For the purpose of illustration atypical embodiment of the invention is shown in the accompanying `drawing in which:

FIG. 1 is a side elevation of a transformer according to the invention;

FIG. 2 is a section on line 2--2 of FIG. 1.

As shown in the figures a lluorescent lamp ballast comprises a core 11 shaped like a rectangular O and formed by two interengaging U-shaped core portions 12 and 13. The upper core por-tion 12 is formed by symmetrical U- shaped, ferromagnetic strips of which ve strips, an outer strip 1 and inner strips 2, 3, 4 and 5 are shown for clarity, although forty-one or more are commonly used. Similarly the lower core portion 13 is formed of five strips, an outer strip 6 and inner strips 7, 8, 9 and 10. The two ends of the strips are staggered in length so that the core portions may be joined with the strip ends in interleafing and butt-engagement. Thus strips 1, 3 and 5 are longer than strips 2 and 4, and `are in butt-engagement with strips 6, i8 and 10', while interleafin-g with strips 7 and 9. The interleaf zone 17 is defined by two planes 18 and 19 respectively, at the spaced ends of strips 7 and 9 and the butting ends of strips 1, 3 `and 5. To improve the performance (crest factor) of the ballast two spaced inner strips 2 and 4 are foreshortened to leave air gaps G between their ends and the ends of strips 7 and 9.

The strips of each core portion are secured together by welds 14 so that each portion comprises two parallel legs 16 and a connecting leg 15. When the c-ore portions are joined the connecting legs 15 and parallel legs 16 surround a space 21 occupied by the windings of primary coils P1 and vP2 and secondary coils S1 and S2. The coils embrace one leg 16 of each core portion with the axis through the coil parallel to the leg 16.

In a ballast numbers of turns and the diameter of the wire in the primary and secondary depend upon the requirements of the lamp which it supplies. Thus the axial lengths of the primary and secondary coils parallel to the legs 16 vary relatively.

With coils P1, P2, S1 and S2 located in the coil space of the two joined core portions 12 and 13, the outer core strips 1 and 6 are connected by weld-s 22 along the line of butt-engagement of strips 1 and 6 thereby securing the upper and lower portions 12 and 13 of each core 11 together. Magnetic shun-t straps 23 are then secured at opposite sides of the core 11 with a bolt 24 and nuts 25, so as to bridge the parallel legs 16 of the core.

As is known in the art the shunt straps are slightly spaced from the core 11 by insulating strips 26 so as to have a high 4reluctance relative to the closed iron path around the core 11. When a lamp is started the shunt is ineffective and full voltage appears across each secondary which is parallel with the luorescent lamp supplied. But once .the arc is established in the lamp, high current in the secondary brings the core 11 toward saturation and flux is shunted through the insulating strips 26 and straps 25 reducing the voltage across the secondary during normal operation.

By locating the air gaps G outside the shunt zone, covering the butt joints in plane 1-9 and the interleaf zone 17, the ballast is most etlicient. The exposed batting ends of strips 1 and 6 can be easily welded after assembly of the coils and core portions, and the previously used connecting straps may be omited. With the relative location of air gaps, butt joints and shunt, `a wide range of primary and secondary coil sizes may be used on the core without loss of efficiency.

While one desirable embodiment of the invention has herein been disclosed by way of example, it is to be understood that the invention is broadly inclusive of any and all modications falling within the terms of the appended claims.

I claim:

1. An inductor comprising two U-shaped magnetic metal core portions forming legs joined to surround a coil space, a plurality of coils of diiferent axial lengths embracing at least one leg of each core portion, and extending through dilferent parts of said coil space, each said core portion comprising at least three U-shaped strips including an outer strip and inner strips nested within said outer strip, the ends of the strips of one portion being staggered for interleafing and butt-engagement with the ends of the strips of the other portion, the outer strips of the two core portions being in butt-engagement outside the embrace of said coils and joined by a fused bond lto secure the portions together, at least one of the inner strips of one portion being spaced endwise from a strip of the other portion to form an air gap therebetween, and a magnetic shunt body extending between parallel legs of said core portions in a Zone coextensive with the interleang ends of the strips, said air gap being located outside said zone.

2. An inductor according to claim 1 wherein said coils and shunt substantially entirely cover said Vcoil space.

3. An inductor accordingto claim 1 wherein said strips are of symmetrical U-shape.

4. An inductor according to claim 1 wherein said air gaps are disposed in a common zone under one of said lcoils.

References Cited UNITED STATES PATENTS 2,350,029 5/1944 Glass 336-178 2,550,501 4/1951 Sims 336-210 X 2,930,997 3/1960 -Fisher et al. 336-210 X 3,128,443 4/1964 Herman et al. 336-160 3,278,878 10/1966 Collucci 336-160 LEWIS H. MYERS, Primary Examiner.

T. I. KOZMA, Assistant Examiner. 

1. AN INDUCTOR COMPRISING TWO U-SHAPED MAGNETIC METAL CORE PORTIONS FORMING LEGS JOINED TO SURROUND A COIL SPACE, A PLURALITY OF COILS OF DIFFERENT AXIAL LELNGTHS EMBRACING AT LEAST ONE LEG OF EACH CORE PORTION, AND EXTENDING THROUGH DIFFERENT PARTS OF SAID COIL SPACE, EACH SAID CORE PORTION COMPRISING AT LEAST THREE U-SHAPED STRIPS INCLUDING AN OUTER STRIP AND INNER STRIPS NESTED WITHIN SAID OUTER STRIP, THE ENDS OF THE STRIPS OF ONE PORTION BEING STAGGERED FOR INTERLEAFING AND BUTT-ENGAGEMENT WITH THE ENDS OF THE STRIPS OF THE OTHER PORTION, THE OUTER STRIPS OF THE TWO CORE PORTIONS BEING IN BUTT-ENGAGEMENG OUTSIDE THE EMBRACE OF SAID COILS AND JOINED BY A FUSED BOND TO SECURE THE PORTIONS TOGETHER, AT LEAST ONE OF THE 